My 1985 4Runner is a DLX model, not an SR5. It had no rear seatbelts or rear wiper among other things.

It has the original interior minus the rear headrests, which I want to replace. Here's the problem. It looks like the seats are made to accept a single post headrest as opposed to the double post ones we are all familiar with. Any knowledge of this?

 

I have never seen one like that. The release knob does look like a factory rear seat. My 86 and a friends 86 also did not come with rear seats and the PO put in some seats from some other model and wonder if that is what they did with yours.